I just posted it as a reply to the SRX brass sounds mentioned, to show their outstanding realism. but I fear very few of the SRX 10 are included in the BK-9. I made an analysis of where the BK-9 on-board tones come from (based on the tone names, which is usually a reliable indicator in case of Roland), and as far as I remember a lot are from SRX09 World, but very, very few from other SRX boards.
For the Roland FA-06/08, you get the SRX expansion for free as a download. I expected something similar for the BK-9, but Roland hasn't fulfilled their announcement to release expansion sounds for the BK-9 yet.
Anyway, IMO you definitely can't say Roland has a general weakness in brass sounds.